1. Field of the Invention
The field of this invention is within the ultrasonic wire bonding art. More particularly, it is within the art of ultrasonically bonding a wire to an underlying substrate such as an electronic part, an electrical part, or a semiconductor. The invention falls into the category of ultrasonically bonding wire in a facile and quick manner.
2. Background of the Invention and Prior Art
The prior art with regard to ultrasonic wire bonding generally included the aspects of having a bonding tool lowered to a wire and applying ultrasonic energy through a transducer. As the ultrasonic energy was applied, a given amount of pressure was provided at the tip of the bonding tool in order to make a solid contact. This pressure was generally provided by certain types of springs, flexures, or other pressure.
The use of such springs and flexures oftentimes did not allow for a suitable pressure on the bond tool while at the same time preventing lateral displacement. This created disadvantages as far as control forces, life of the flexure, maintenance, and axial and spring force offsets. Many of such flexures and springs were based upon being formed as a parallelogram.
This invention overcomes the deficiencies of such flexures by having a spring system with an inner cylinder and an outer cylinder. The two respective cylinders can be generally described as an inner cylinder supported on a ring or outer cylinder at an upper and lower end. The ring flexes upwardly and downwardly through its bending moment.
The spring and ring configuration can be made of a number of arcuate arms preferably three in number in approximately 120xc2x0 arcuate segments. The arc shaped portions of the ring or beam provide for a greater free movement. At the same time they provide relative stability with regard to the end of the bond tool or other components to which they are attached.
The invention specifically utilizes two respective rings that are formed as stacks, disks, or sheets of material such as metal substantially perpendicular or normal to the axis of the tools and Z axis of the bonder.
The use of small stacks of flexures or ring segments is in the form of two or three stacked portions. Each one respectively provides for an improved degree of stiffness while at the same time providing sufficient flexure to create the proper displacement.
One of the problems of the prior art was the articulation of the wire clamps and the design of wire guides. With the increased tightness of looping of wires from one bond to another along with lower height loops and pull tests, the disadvantages of the prior art have become pronounced. Further to this extent, the opening and closing of the wire clamps was usually done on a mechanical basis. Time was spent when substantially rapid movement was required for moving from one bond to the next. This is particularly true when considering the pull test function wherein wires are pulled in order to test the strength of the bond.
In order to improve the speed of the opening and closing of the wire clamps, this invention utilizes a coil and magnet system. They are driven to open and close the clamps thereby reducing inertia and other characteristics of movement that slowed down the movement. The clamp force is also able to be controlled by software.
In order to do this, a coil and magnet such as a voice coil combination is attached to the bond head and moves in the Z axis. When the voice coil is energized, the beam, link, or lever on which it sits moves about a pivot point rotating the clamps. When the coil is pushed downwardly, it opens the clamps and when the coil is moved upwardly, it closes the clamps.
The foregoing functioning elements reduce friction loses, inertia and other characteristics that were encountered in the prior art.
Another improvement is that the wire guide is designed so that it fits around the clamps, or alternatively stated the clamps are within the wire guide.
All of the foregoing provides for improved features as to the mechanical movement, speed, and accuracy of the clamps providing various programmable clamp forces. Further to this extent, the wire guide and the fixed clamp cut down on manual adjustments inasmuch as there is only one moving part. Finally, when the clamps are inserted into the wire guide, the opening distance is automatically established.
Another problem with the prior art is that the cutter in order to cut the wire was in a laterally displaced relationship to the bond tool. In order to provide for a cut when the Z axis movement is encountered, the space between the bond tool and the cutter created a larger length of wire remaining than was desired. In order to cure this, a motion, pushing, or movement of the cutter toward the bond tool is desirable.
In order to accomplish this, a drive for the cutter blade in this invention causes it to be pushed or moved toward the bond tool during the cutting motion when it moves in the Z axis. This is done by a piezoelectric stack that moves the cutter blade around a flexure point. When movement is encountered, it moves the cutter into sufficiently close proximity to the bond tool. This helps to eliminate the larger tail encountered if a space were opened significantly between the bond tool and the cutter.
By using the piezoelectric stack with a flexure pivot point, it allows the articulation of the cutter to follow the front surface of the bond tool during the cut. This provides for improvement of the front cut of the wire thereby creating improvements with regard to wire bonding on very small surfaces such as semiconductors.
For the foregoing reasons, it can be seen that this invention has numerous features that solve the problems of the prior art that have not been solved to this point.
In summation, this invention comprises a novel large wire ultrasonic bonding head having highly improved flexural support for the bonding elements with an improved wire clamp and wire guide and further incorporating an active laterally moving cutter for the wire.
More specifically, the flexure assembly comprises an outer ring or supporting spring flexure formed of multiple arcuate arms and an inner cylinder portion supported on the arcuate arms. The inner portion supports the active components of the wire bonding elements. This includes the bonding tool, the wire clamps, and the wire feed. The support of the bonding elements on the circular ring creates an improved spring decoupling function while at the same time reducing lateral displacement, and eliminating friction. Further improvements include the use of a fillet at the connection point of the spring members or arcuate arms to reduce fatigue, and a pocket into which they can bend or flex.
The wire clamps and wire guide are improved by virtue of the wire clamps being actively driven by a programmable coil and magnet which can be referred to as a voice coil. In this manner, the clamps can be driven as to clamping movement and timing over a broad range while at the same time providing faster wire clamping action.
A wire guide surrounds the clamps and seats the clamps therein. The wire guide is suspended on the fixed arm of the clamp and provides for improved connection of the wire guide and ease of adjustment.
An active laterally displacing member for the cutter blade is utilized which moves the cutter blade into close proximity with the bonding tool. This is performed by a piezoelectric stack or any other active moving means to place the cutter into a closer proximity with the bond head. Close cropped cuts of wire can be performed for improved bonding in narrow and reduced areas of semi-conductors and other electronic components.
From the foregoing summary and background of the invention it will be seen in light of the following description of the preferred embodiments that this invention is a significant step over the art of wire bonding heads.